Add chromeos_glossary.md

Change-Id: Ie227a7fa799c50db4f874ea2a82d1c0b1bcad5a0
Reviewed-on: https://chromium-review.googlesource.com/c/1448511Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Auto-Submit: Ned Nguyen <nednguyen@google.com>
Commit-Queue: Dirk Pranke <dpranke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#628488}

docs/chromeos_glossary.md

+See [Chromium OS Glossary](https://chromium.googlesource.com/chromiumos/docs/+/master/glossary.md)